1. Field of the Invention
The present invention relates to plasma display panel display devices, and particularly a plasma display panel display device capable of reducing unwanted radiations that occur during the driving and discharge of a plasma display panel.
2. Description of Related Art
Because of advantages including a large screen size and a thin screen, plasma display panel display devices have been well-spread in recent years.
With reference to FIG. 4, conventional plasma display panel display devices are described below in regard to structure and image display operation. FIG. 4 is a lateral cross sectional view showing a schematic illustration of a structure of a conventional plasma display panel display device 100. As shown in FIG. 4, the display device 100 includes a plasma display panel (front panel) 1 that forms an image.
The plasma display panel 1 includes sustain discharge electrodes (hereinafter “X electrodes”) and sustain-scan discharge electrodes (hereinafter “Y electrodes”), extending in the width direction of the plasma display panel, and disposed along the height direction of the plasma display panel in numbers corresponding to the number of display lines. The plasma display panel 1 also includes address electrodes that perform scan and discharge with the Y electrodes. The address electrodes are provided to cross the Y electrodes orthogonally, in numbers corresponding to the number of display dots. A discharge cell is formed at each intersection where the X electrodes and the Y electrodes cross the address electrodes.
As shown in FIG. 4, the display device 100 also includes: an aluminum chassis 2 disposed on the rear side (lower side in FIG. 4) of the plasma display panel 1; a substrate 3 provided with an X electrode driving circuit used to apply a driving pulse waveform to the X electrodes; a substrate 4 provided with a Y electrode driving circuit used to apply a driving pulse waveform to the Y electrodes; a flexible wiring substrate 5 connecting the X electrode driving circuit to the X electrodes; and a flexible wiring substrate 6 connecting the Y electrode driving circuit to the Y electrodes.
In the display device 100, an electrical interconnection is made between the ground of the X electrode driving circuit and one end of the aluminum chassis 2 (left end in FIG. 4), and between the ground of the Y electrode driving circuit and the other end of the aluminum chassis 2 (right end in FIG. 4).
For the driving of the display device 100, a sub-field driving method is used commonly, which controls display gradations by the number of discharges. Each sub-field includes a reset period, an address period, and a sustain discharge period.
The following describes an operation of the display device in each period. In the reset period, a reset pulse voltage is applied between the X electrodes and the Y electrodes to cause discharge in all pixels and erase the remaining wall charge of the previous sub-field. In the address period, a scan pulse is applied successively to the Y electrodes, and at the same time, an address pulse voltage is applied to the address electrodes of the pixels corresponding to the video display content, thereby causing address-discharge between the Y electrodes and the address electrodes to accumulate wall charges. In the sustain discharge period, a sustain-discharge pulse voltage is applied between the X electrodes and the Y electrodes to cause sustain-discharge in the pixels that accumulated the wall charges during the address period.
Due to the sustain discharge, vacuum ultraviolet rays are generated in the pixels. The vacuum ultraviolet rays irradiate the phosphors provided in the pixels, causing the phosphors to give off visible light and lighting the pixels. In the sustain discharge period, a driving voltage of several hundred volts and several hundred kHz is applied alternately to the X electrodes and the Y electrodes to cause discharge in the pixels between the electrodes. As a result, a large impulse current flows in the front panel during the sustain discharge period.
For example, applying a driving voltage to the X electrodes creates a large current flow in a loop path formed by the driver of the X electrode driving circuit, the X electrodes, the atmosphere in the pixels, the Y electrodes, the ground of the Y electrode driving circuit, the aluminum chassis 2, and the ground of the X electrode driving circuit. The large current in the loop generates a strong magnetic field, which is the primary cause of unwanted radiation in the display device.
JP2005-221797A discloses a plasma display device intended to reduce such unwanted radiation. In one aspect, JP2005-221797A discloses a device (first device) including: a plasma display panel having electrodes for causing discharge; a plurality of driving circuits for applying a voltage to the plasma display panel; a first wiring that interconnects the plasma display panel and the driving circuits; and a second wiring that interconnects the driving circuits by forming a first loop behind the driving circuits on the rear side of the plasma display panel, the magnetic field generated by a current flowing in the first loop being directed in the opposite direction from the magnetic field generated from a second loop formed by the driving circuits and the plasma display panel (claim 1). As shown in FIG. 6, in a device 400 of this publication, driving circuits 402 and 403 are connected to each other with a connector cable 404 of a size suited to connect these driving circuits. As shown in FIG. 6, the width of the connector cable 404 is considerably narrower than the height of a plasma display panel 401 (length along the vertical direction in FIG. 6).
In another aspect, JP2005-221797A discloses a device (second device) including: a plasma display panel having electrodes for causing discharge; a chassis disposed behind the plasma display panel; a conductive member disposed in front of the plasma display panel; and a plurality of driving circuits for applying a voltage to the plasma display panel, the magnetic field generated by a current flowing in the plasma display panel and the conductive member in response to the applied voltage from the driving circuits being directed in the opposite direction from the magnetic field generated by a current flowing in the plasma display panel and the chassis in response to the applied voltage from the driving circuits (claim 4). In a device 500 of this structure, when a plasma display panel 501 is driven by applying a voltage from driving circuits 502 and 503, a current that flows in the panel 501 branches into a conductive member 504, disposed in front of the panel 501, and a chassis 505, disposed behind the panel 501, as shown in FIG. 7.
In yet another aspect, JP2005-221797A discloses a device (third device) including: a plasma display panel having electrodes for causing discharge; a plurality of driving circuits for applying a voltage to the electrodes of the plasma display panel; a chassis interposed between the plasma display panel and the driving circuits; and metal boards paired with the driving circuits, the magnetic field generated by a current flowing in the plasma display panel and the chassis being directed in the opposite direction from the magnetic field generated by a current flowing in the driving circuits and the metal boards (claim 6). In a device 600 of this structure, as shown in FIG. 8, a driving circuit 602 and a metal board 604 are disposed at one end (left end portion in FIG. 8) on the rear surface of a plasma display panel 601, and a driving circuit 603 and a metal board 605 are disposed at the other end (right end portion in FIG. 8) on the rear surface of the panel 601. In this device, the magnetic field that cancels the magnetic field generated between the panel 601 and the chassis 606 is generated only in the vicinity of the ends of the panel 601.
The devices disclosed in JP2005-221797A are intended to reduce unwanted radiation by canceling the magnetic field components. However, it is difficult to reduce unwanted radiation sufficiently with these devices.
Regarding the first device, as shown in FIG. 6, since the connector cable is considerably narrower in height than the plasma display panel, the magnetic flux generated from the first loop and the magnetic flux generated from the second loop originate and terminate at different heights (vertical positions in FIG. 6), making it difficult to cancel out the magnetic field components generated in the device sufficiently.
In the second device, because the first and second current loops are formed by dividing the current from the plasma display panel, it is difficult to create the same current intensity in these current loops. Accordingly, it is difficult to cancel out the magnetic field components generated in the device sufficiently.
In the third device, as shown in FIG. 8, since the driving circuits 602 and 603 and their respective metal boards 604 and 605 are disposed only at the left end portion and right end portion, respectively, of the panel 601, the magnetic field generated between the panel 601 and the chassis 606 will not be cancelled sufficiently at the lateral middle portion of the panel 601.